This invention relates to high speed printers and more specifically, it relates to a stacker that can handle both a single sheet and multiple sheets as they come up.
In many automatic copying or printing machines, rotating disk stackers are often used for providing combined sheet inversion and stacking of output copy sheets. In a typical rotating disk stacker, copy sheets are sequentially transported into an arcuate receiving slot on a rotating disk. The copy sheet lead edge is inserted into the receiving slot and the copy sheet is temporarily maintained in contact with the rotating disk such that the rotating movement of the disk flips the sheet over and simultaneously guides the inverted sheet into a collecting tray. Inverted sheet stacking devices of this type, sometimes referred to as xe2x80x9cwindsor stackersxe2x80x9d, are well known and have been disclosed, for example, in commonly assigned U.S. Pat. Nos. 4,385,756, 5,058,880, 5,065,996, 5,114,135, 5,409,202, 5,476,256, and 5,551,681 among others. The disclosures of these patents are hereby incorporated by reference in their entirety.
Customer requirements for printer output speeds are constantly increasing. One way to increase the speed of the printer, without increasing the speed of the xerographic module, is to print two-up. Printing two-up involves printing two images side-by-side on the same large sheet (11xe2x80x3xc3x9717xe2x80x3 for example). Then, after the sheet is printed, it is fed into a slitter module, which slits the sheet into two smaller sheets (8.5xe2x80x3xc3x9711xe2x80x3). Two sheets arrive xe2x80x9ctwo-upxe2x80x9d at the next device. This effectively doubles the output speed of the printer.
Since most printers embody digital technology, the images on each side of the sheet can either be duplicates or prints from separate jobs. However, printing two-up creates problems after the slitting has occurred because now there are two sheets traveling side-by-side through the paper path. Current stackers have difficulty handling two sheets at once.
At least two methods have been used to stack sheets that are printed two-up. In some machines, the paper paths of the sheets are merged so that one of the sheets is moved such that it is on top of the other. This method is shown schematically in FIG. 1. In other machines, the sheets are sequenced by changing the direction of travel of the sheets by 90xc2x0. This method is shown schematically in FIG. 2. The sheets arrive at the sequencer in parallel, but continue in a sequential order. Both of these options require an expensive module for preparing the sheets to be stacked.
Disclosed embodiments include a sheet-stacking apparatus, which includes four substantially identical similar, rotatable disks; wherein each disk includes a receiving slot for receiving a portion of a sheet therein; a disk rotation system that rotates the four disks; a selectively extendable separator; and an actuator for selectively extending the separator when at least two sheets enters the stacker at substantially the same time and retracting the separator when a single sheet enters the stacker.
Embodiments include a shaft connected to each of the four disks and about which each of the four disks rotates and a stepper motor operably connected to the shaft for rotating the shaft.
Embodiments also include a controller operably connected to the actuator, wherein the controller causes the actuator to extend or retract the separator.
Embodiments also include a method for stacking sheets arriving in a two-up manner, which includes rotating a first sheet of paper with a first pair of disks until the first sheet is inverted; rotating a second sheet of paper with a second pair of disks until the second sheet is inverted, wherein the first sheet and the second sheet are rotated substantially simultaneously; and separating the first sheet from the second sheet with a selectively extendable separator.
Embodiments also include a stacking apparatus, which includes first, second, third, and fourth substantially similar disks, each disk having a substantially common axis of rotation with the others, wherein each disk includes a receiving slot for receiving a portion of a sheet therein, and wherein said first, second, third, and fourth disks are coaxial; a disk rotation system that rotates said first, second, third, and fourth disks; a selectively extendable separator; and an actuator for selectively retracting the separator when at least one sheet having a first width enters the stacker and extending the separator when at least one sheet having a second width enters the stacker.
In embodiments, the first, second, third, and fourth disks are symmetrically arranged into two pairs of disks, with said first and second disks on one side of the separator and said third and fourth disks on another side of the separator when the separator is extended.
In embodiments, the second width is approximately half the first width.